Electrical insulation material



Patented July as. 1936 h 2,049,370

UNITED STATES PATENT OFFICE HECTRICAL-INSUIATION MATERIAL Frank .I. crotch, Pittaileld, this, assignor to General Electric Company, a corporation of New York No Drawing. Application June 30, 1934, Serial N0. 733,329

3 Claims. (CI. 91-70) The present invention relates to electrical inweight 'of paraflln wax are employed. These suiation material, and more particularly to the waxes are heated together until solution takes treatment of asbestos board in such a manner place and held at 300 F. at which temperature that its insulating properties, and moisture resistthe asbestos board panels are impregnated. Com- 5 anee are markedly improved and at the same plete impregnation of a 1 inch panelusualiy takes 5 time maintaining its maximum arc resistance. Place in about 48 to 96 hours.

Asbestos board consists largely of asbestos In order to illustrate how eflectively the ashesbonded together with a mineral binder such as tos panel board material of the present inven- Portland cement. It is used in sheets having a tion maintains the arc resistance at the value thickness of about inch to 2 inches. One of iv by unt at as st s a d in mpa n 10 the principal uses for such board is as a switchwith the results obtained on a standard panel board panel material and in this connection itls board material herein des t as X t very essential that the material withstand mois-, lowin tests Were carried ut. ture and the action of an electrical are. If the An electrode arrangement consisting o W0 #8 material carbonizes under the influence of an brass machine screws with b" 0- Wash- 16 'electrical arc and permits tracking its value as r nder th S rew heads was used. These an insulation material under these conditions is .s ws were pla d in two holes dr ll d throu lost. the test specimens on one inch centers. Nuts Asbestos board has heretofore been impregon these screws were drawn up tight to make 2o nated with material such as asphalts and it hes good contact between the washers and the surface 20 v and while these materials have rendered the of the speeim The pp i e clearance board moisture resistant such impregnation rebetween washers was 9Q". L

suits in marked decrease in arc resistance of the To simulate service conditions where a severe asbestos board. arc is often started at moderate voltages by dirt In accordance with the present invention it accumulated on the surface of thepanel, graph- 25 v has been found that if asbestos board is impregite was sprinkled on the test specimen between nated with certain waxes in certain proportions the electrodes, the surface of the specimen being that the maximum arc resistance of the board is horizontal. Voltage was then applied, being maintained. raised gradually from zero to the value n In order to illustrate the invention the foltoiiashover the electrodes. r 30 lowing example of the manufacture of a switchwith the material designated X flashover 0oboard panel isgiven: curred at 1500 volts and the material carbonized The asbestos board is given a wax dip in a immediately. After cooling of! slig y, the mixture o earnouboand p fl wa The application of a voltage of from 90 to 150 volts proportions of these waxes are chosen such that caused. sparking. Sparking still occurred at this 5 Just enough D fl wax is employed h the value after brushing and blowing away all free carnauba wax in rd t cause t s 'p graphite, showing that a highly conducting cartration of the mixture through the board. It has v n path had been formed through t been found that if carnauba wax is used by itself terigl between t l t des,

40 only surface penetrotion of the board results With the material of the present invention and to giving a non'unflormly impregnated Panel boardwith graphite between the electrodes arc over oc- It has also been discovered that the paraffin wax curred 400 t mg slightly lower w. as came? m cause the waxes to thoroughly age value was due to the fact that in this particupenetrate the panel board Thus while pamfim iar test a little excess of graphite over that used I wax is ordinarily avoided in electrical insulation in the preceding test happened to be placed. 45

mggr g fi xi gg zgi if g fi' fi tween the electrodes.) After arcing for several in conjunction with carnauba wax to cause the mmutes wlth no apparent damage to board? latter to penetrate the asbestos board and to give the arc was interrupted" excess gmpmte was w 223533 e massa es: more: aa-

an an are re s ance. as n oun t t thi ixt of waxes 111 t track even at 4000 volts but the sparking soon cleared. This under severe arcing conditions. operation was repeated several times at succeed- As a'preferred mixture of waxes to use, two ingly hi her voltages- T m e l with parts by weight of carnauba wax to 1 part by these higher voltages until the air flashover of 56 10,500 volts (for this electrode spacing) was reached.

The above test has been repeated a number oi. times in various places including steel mills and the same results obtained each time, namely, the impregnated asbestos board oi the present invention would not carbonize and was not electrically damaged by the arc, whereas in all cases standard panelboard material consisting essentially of the same base asbestos board, but which were filled with pitches and the like, carbonized very quickly and were permanently electrically damaged.

What I claim as new and desire to secure by Letters Patent oi the United States, is:-

1. An electrical arc-resistant insulator consisting of asbestos board containing a wax mixture throughout its surface and interior, said wax mixture being composed of two parts by weight of carnauba wax and one part by weight 01 parafiin wax.

2. The method oi. maintaing the maximum arc resistance of asbestos board and improving its moisture resistance which comprises immersing the same at 300 F. in a mixture of carnauba wax and paraflin wax in proportions such that the latter carries the waxes into the board beyond surface penetration, and continuing the immersion until complete penetration of the board by the waxes takes place.

3. A switchboard panel consisting of a board of substantial thickness composed largely of asbestos bonded with Portland cement, said board being surface coated and impregnated throughout its entire thickness with a mixture consisting of camauba wax and paraflln wax in proportions such that the latter carries the entire wax mixture through the surface and into the entire board thickness.

FRANK J GROTEN. 

